Etymology
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aconite (n.)

poisonous plant (also known as monkshood and wolfsbane), 1570s, from French aconit (16c.), from Latin aconitum, from Greek akoniton, which is of unknown origin.

The highly poisonous alkaloid in it, once isolated, was named aconitine (1826). The ancient folk-etymology of the name is Derived by the ancients from Greek akoniti "without dust," hence "without struggle or fight," hence "invincible" in its deadly effect. But Beekes finds this "hardly possible" and proposes a substrate origin.

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acorn (n.)

Middle English akorn, from Old English æcern "nut, mast of trees, acorn," a common Germanic word (cognates: Old Norse akarn, Dutch aker, Low German ecker "acorn," German Ecker, Gothic akran "fruit"), originally the mast of any forest tree. It is by most sources said to be related to Proto-Germanic *akraz, the source of Old English æcer "open land," Gothic akrs "field," Old French aigrun "fruits and vegetables" (from Frankish or some other Germanic source), perhaps on the notion of  "fruit of the open or unenclosed land;" see acre.

The sense was gradually restricted in Low German, Scandinavian, and English to the most important of the forest produce for feeding swine: the mast of the oak tree. The regular modern form would be *akern; the current spelling emerged 15c.-16c. by folk etymology association with oak (Old English ac) and corn (n.1), neither of which has anything to do with it. Acorn squash is attested by 1937.

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acoustic (adj.)

c. 1600, "pertaining to hearing or sound," from French acoustique, from Latinized form of Greek akoustikos "pertaining to hearing," from akoustos "heard, audible," verbal adjective from akouein "to hear," which probably is from copulative prefix a- (see a- (3)) + koein "to mark, perceive, hear" (from PIE root *kous- "to hear," which is also the presumed source of English hear).

In reference to material meant to deaden sound, 1924. Of sound reproduced mechanically (rather than electrically) from 1932 in reference to gramophone players; acoustic guitar (as distinguished from electric) is attested by 1958. Related: Acoustical; acoustically.

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acoustics (n.)

1680s, "the science of sound," from acoustic; also see -ics. The meaning "acoustic properties" of a building, etc., is attested from 1885.

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acquaint (v.)

early 13c., "make oneself known" (reflexive, now obsolete); early 14c., "to gain for oneself personal knowledge of," from Old French acointer "make known; make or seek acquaintance of," from Vulgar Latin *accognitare "to make known," from Latin accognitus "acquainted with," past participle of accognoscere "know well," from ad "to" (see ad-) + cognitus, past participle of cognoscere "come to know" (see cognizance).

Meaning "to inform (someone of something), furnish with knowledge or information" is from 1550s. Related: Acquainted; acquainting.

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acquaintance (n.)
c. 1300, "state of being acquainted;" late 14c., "person with whom one is acquainted;" also "personal knowledge;" from Old French acointance "acquaintance, friendship, familiarity," noun of action from acointer "make known" (see acquaint). Acquaintant (17c.), would have been better in the "person known" sense but is now obsolete. Fowler regards acquaintanceship (1792) as a "needless variant."
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acquainted (adj.)

early 13c., "personally known;" past-participle adjective from acquaint (v.). Of skills, situations, etc., from late 15c.

I have been one acquainted with the night.
I have walked out in rain — and back in rain.
I have outwalked the furthest city light.
[Robert Frost, from "Acquainted with the Night"]

Acquaint also was used as an adjective (late 13c.) "acquainted."

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acquiesce (v.)

1610s, "remain at rest" (a sense now obsolete); 1650s as "agree tacitly, concur," from French acquiescer "to yield or agree to; be at rest," (14c.), from Latin acquiescere/adquiescere "become quiet, remain at rest, rest, repose," thus "be satisfied with, be content," from ad "to" (see ad-) + quiescere "become quiet," from quies (genitive quietis) "rest, quiet" (from PIE root *kweie- "to rest, be quiet"). Related: Acquiesced; acquiescing.

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acquiescence (n.)

1630s, "rest, quiet, satisfaction," from French acquiescence, noun of action from acquiescer "to yield or agree to; be at rest" (see acquiesce). Meaning "silent consent, passive assent" is recorded from 1640s.

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acquiescent (adj.)
"disposed to yield, submissive," 1690s (implied in acquiescently), from Latin acquiescentem (nominative acquiescens), present participle of acquiescere "become quiet, remain at rest" (see acquiesce).
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